The present invention generally relates to waste comminutors and, more particularly to waste comminutors having cutter elements with additional surfaces for the shearing or cutting of waste particles.
Comminutors are mechanisms that are used to reduce the particle size of solid waste material. The reduction in size is typically accomplished by a shearing, crushing, shredding action or the like which is performed by one or more rotating elements of the comminutor. Comminutors are most often used in the field of wastewater treatment to reduce the size of solid waste particles entrained in wastewater influent streams. Smaller particle size promotes more efficient treatment of the wastewater. Comminutors are also used in applications to reduce particle size of solid waste which is not entrained in a liquid solution.
Early comminutors utilized a relatively large rotating component formed from a series of spaced-apart discs which form a rotating screen. The screen has a series of cutting teeth mounted on its exterior at different locations which project therefrom and which extend through corresponding slots formed in a cutter bar held by the support frame of the comminutor. An example of such a comminutor is shown and described in U.S. Pat. No. 2,336,069, issued December 1943 to applicant's predecessor in interest, Chicago Pump Company. The comminutor shown in this patent is know as a "flow-through" comminutor where waste material particles impinge upon the rotating screen and are moved into contact with the cutter bar by the teeth of the screen where small pieces of the waste particles are cut or sheared from the waste. These style of comminutors perform their intended function very well. However, because they utilize a single rotating screen, flow-through comminutors require a relatively large space in a waste stream channel.
Other comminutor designs are more compact and utilize a pair of spaced-apart parallel cooperating rotating shafts which support a series of cutting elements or discs. Such a dual shaft comminutor structure is disclosed U.S. Pat. No. 4,046,324, issued Sep. 6, 1977. This comminutor utilizes two shafts, each of which contains a cutting or shredding assembly formed by multiple cutter and spacer elements arranged axially on the shaft in alternating fashion so that on each shaft any cutter element is spaced apart from any axially adjacent cutter by an intervening spacer which defines a series of annular open spaces. Each open space between adjacent cutter elements on one shaft receives an opposing cutter element from the other shaft. Thus, the cutter elements are staggered to form pairs of interactive comminuting elements in which a cutter element and spacer element are coplanar.
In a dual shaft comminutor, waste particles are sheared or cut apart in two fashions. In one fashion, they may be caught in the pairs of interactive comminuting elements between the outer circumferential edges of the cutter elements and the spacers which oppose them on the other shaft. In the second fashion, waste particles may be caught between the opposing planar surfaces of the cutter elements of the shafts. The comminuting action occurs in this second instance between the leading edges of the cutter elements. The counter-rotation of the cutter elements by the shafts provides the needed drive for the crushing, shredding, shearing and cutting actions which the cutters perform. However, there has been no attempt to increase the efficiency in such comminutors thereof by increasing the total number of comminuting surfaces of the comminutor or by providing the comminutor with any pumping characteristics. Additionally, dual shaft comminutors of the prior art do not include any means for self-cleaning.
The present invention is therefore directed to a waste comminutor having improved cutter elements which increase the total number of comminuting surfaces of the comminutor. The present invention is also directed to a waste comminutor in which the cutter elements provide a pumping action to reduce head loss through the comminutor and provide a self-cleaning action to dislodge particles from the cutter elements during operation.
Accordingly, it is an object of the present invention to provide a waste comminutor having cutter elements with additional contact surfaces against which waste particles are comminuted, the additional contact surfaces augmenting the efficiency of the comminutor.
Another object of the present invention is to provide improved cutter elements for use in waste comminutors, wherein the cutter elements include disc body portions having opposed planar surfaces with interruptions thereon such as pockets, recesses or the like in a cutting zone in the area where opposing shaft-mounted cutter element opposed planar surfaces overlap during operation.
Yet another object of the present invention is to provide an improved waste comminutor having a pair of counter-rotating comminuting assemblies disposed within a comminution chamber of the comminution, each assembly including a plurality of cutter elements axially arranged along the rotating shaft and separated by intervening spacer elements, the cutter elements having a series of pockets formed in exterior opposed, planar surfaces of the cutter elements radially outwardly of the spacer elements in the area wherein the cutter elements of the comminuting assembly overlap, the pockets providing additional surfaces against which waste particles may be cut or sheared.
Still another object of the present invention is to provide cutter elements for a waste comminutor having a circular body and an opening which receives a drive shaft therethrough for mounting the cutter element in the comminutor, the cutter element body having a thickness extending between two opposing planar surfaces, the body further having a series of recesses within the opposed surfaces annularly disposed in the body portion, and separated by intervening vanes which are generally aligned with the drive shaft upon which they are mounted, the vanes imparting a centrifugal force to waste particles and the stream of waste entry entering the waste comminutor so as to provide a self-cleaning action to the teeth of the cutting elements of the comminutor during operation.
Yet a still further object of the present invention is to provide a dual-shaft comminutor having two parallel, counter-rotating cutter assemblies comprised of alternating cutter and spacer elements axially arranged upon the two shafts, wherein the cutter elements are provided with flow directing means in the form of impeller vanes in addition to the cutting teeth thereof, the impeller vanes assisting in pumping a waste stream into the comminutor and promoting a self-cleaning action within the cutter elements.
The present invention accomplishes these objectives by providing a comminutor having two cutting assemblies mounted on two parallel, spaced apart cooperating drive shafts. The cutting assemblies include a plurality of cutter elements and spacer elements axially arranged on each drive shaft such that the cutter elements are separated by intervening spacer elements. The cutting assemblies of the two shafts are interengaged with each other such that the cutting elements of one shaft directly oppose the spacer elements of the other shaft in the same general plane and vice-versa. The cutter elements have opposed generally planar surfaces and a preselected thickness extending between the opposed surfaces such that the cutter elements of the two shaft cutting assemblies overlap each other.
Surface interruptions are defined in the opposed surfaces of the cutter elements and are disposed within the cutting zone of the cutter elements. This cutting zone generally occupies the area in which overlap between opposing cutting assembly cutter elements occurs and generally radially outwardly of the adjoining spacer elements but within teeth formed in the cutter elements at their outer circumferential edges. The surface interruptions may take the form of depressions, pockets, recesses or the like. These pockets collect and hold, or trap, waste particles passing through the comminutor and provide a surface within the comminution chamber which is parallel to the spacer elements separating adjacent cutting elements. The pockets hold the particles in place in a position for additional shearing which occurs in the horizontal plane of the comminutor. These additional shearing surfaces increase the overall efficiency of the comminutor and further provide a means to comminute waste particles of the type which promote clogging of the cutter elements, such as fibrous materials.
The pockets formed in the cutter elements include a base surface or floor which defines the depth of the pockets. The floor surface intersects at least one sidewall of its pocket to form a perimeter portion of the pocket and present a surface angularly offset from the cutter element opposed planar surfaces against which the waste particles are sheared by an adjoining cutting element. The floor surfaces of the pockets may be planar or may be sloped to permit waste particles to easily enter into the pockets and, after shearing exit out of the pockets during operation of the comminutor. The pockets are formed within the cutter elements proximate to the cutting elements and cutting teeth.
The surface interruptions formed in the cutter element body may also take the form of waste stream flow enhancing and directing means, such as spiral recesses or grooves which spiral outwardly from a hub portion and terminate near the circumferential edges of the cutter elements. These spiral recesses are disposed annularly around the hub portion and are separated by intervening land portions which effectively define impeller vanes in the body portions of the cutter elements. These vanes include sidewalls which intersect with a base or floor portion of the recesses such that the sidewalls of the vanes also present additional shearing surfaces against which waste particles may be comminuted.
The impeller vanes and their corresponding recesses not only define additional waste particle contact surfaces, but also define flow-direction means which impart pumping action to the comminutor which consequently reduces the head loss typically associated with comminution. This pumping action imparts a centrifugal force upon the waste stream entering the comminutor, whether the waste stream is entrained in liquid or not, and serves to fling waste particles away from the recesses to promote a self-cleaning action to the cutter elements.
These and other features, objects and advantages of the present invention will become more apparent from a reading of the following detailed description.